Sintered ceramic tiles have got a higher temperature capability than thermal barrier coatings (TBC), which are frequently used in the hot gas path of gas turbines. Thus, for insulation purposes thicker ceramic tiles can be used as thermal protection before application limits are reached. This, in turn, allows for increased cooling air savings for the part, which is beneficial for the overall efficiency of the machine.
However, joining of ceramic tiles to base metal structure is a challenge. They cannot be sprayed like TBCs onto the surface of base metal structure as they require sintering at temperatures beyond base metal melting temperature. Thus, pre-manufactured sintered ceramic tiles must be joined to the base metal structure.
Prior art of joining is—among other technologies—bonding of ceramic tiles to a base structure (e.g. U.S. Space Shuttle). Means of bonding are for example cements or brazing.
Such a joining of ceramic tiles to base metal structure requires low shape tolerances of joint partners and suitable braze connecting metal and ceramic. Residual shear stresses often result in cracking and failures next to the joint.
Other technologies are also known in the art:
Document U.S. Pat. No. 3,918,255 discloses a gas turbine power plant, wherein a metal combustion chamber cylinder is lined on its inside with two layers of ceramic material. The radially innermost layer is an interlocking, tile-like structure of dense ceramic material providing good thermal shock resistance. The intermediate layer which is disposed between the metal cylinder and the innermost layer is a low density ceramic material providing high thermal insulation. The layers of ceramic material are supported by ceramic tubes extending from the outer metal cylinder of the combustor through the intermediate wall and the inner wall. The tubes are also used to direct cooling air into the combustion chamber and increase the turbulence of the burning fuel and air within the chamber.
Document JP 59004824 A discloses a structure in which a tile-shaped ceramics member is arranged at the surface of the metal inner cylinder of a hot gas turbine combustor, said metal surface of the inner cylinder is covered by a ceramics layer with a porosity of 8-30%. The applied ceramics layer is of porous material and preferably has such a value as approximating to the coefficient of thermal expansion of the metal structure. As examples for the ceramics, yttria (Y2O3), stabilized zirconia (ZrO2), magnesia (MgO), calcia (CaO) etc. are applied. In case that the porosity of the ceramic layer is less than 8%, tacky peeling of the layer may easily be made, and in turn if it exceeds 30% or more, cohesion aggregation peeling of the layer may easily be made. The thickness of the ceramics is preferably in a range of 0.1-0.5 mm.
Document EP 0 658 724 A2 discloses a combustion chamber, in particular for gas turbines, with a hollow-cylindrical supporting wall, on the inside of which a lining composed of individual ceramic elements is arranged, the ceramic elements being designed as trapezohedrons, the base areas of which are adapted to the geometry of the combustion chamber and are fastened to the inside of the supporting wall.
Document US 2011/0123323 A1 discloses an assembly for use in a gas turbine engine that has an underlying metal sheet, and at least one ceramic matrix composite tile attached to the underlying metal sheet with at least one fastener assembly. The panel fastener assembly includes a fastener having a threaded portion extending rearwardly from a head, which has a frustoconical surface facing the threaded portion. The frustoconical surface is received in a frustoconical bore in the ceramic matrix composite panel. A bushing is positioned on an opposed side of the metal sheet from the ceramic matrix composite panel. The bushing has a flange extending away from the metal sheet. A sleeve is received about the threaded portion of the fastener, and extends away from the panel, beyond the metal sheet. The sleeve has a lip extending radially outwardly toward the flange on the bushing, such that the flange on the bushing extends beyond a space defined between the lip and a seating surface on the bushing. A wave spring is received within the cavity.
Several other documents, for example abstracts of JP H04 119974 A, JP H01 99767 A or JP S60 155579 A disclose forming ceramic-metal composite material or workpieces by casting molten metal on a ceramic with interlocking joints.
On the other hand, it is known from document US 2011/0243724 A1 that a metal-to-metal joint can be established by so called bi-cast process.
However, there is still a need for a process of manufacturing a metal-ceramic composite structure, especially for components being used in the hot gas path of a gas turbine, which process results in structures of superior mechanical stability and high temperature capability.